280 C. Barus — Method for the Observation of Coronas. 



Since the elementary diffraction equation may be put 



sin = 1-22 X/d 



for the first minimum 



S X . , 



and xS* would therefore appear to be less immediately adapted 

 for the equation than s. It does not follow, however, that this 

 s and the one observed at the goniometer work are the same. 

 In fact they are not, the latter being larger for reasons involved 

 in the more recondite theory of the experiment, or else due to 

 irregular refractions at the remote ends of the chamber. 



5. Remarks on the results. — Without entering at length into 

 the details of the subject, it is clear that if ds= a for normal 

 coronas, where d is the diameter of particles and a an optical 

 constant, s — a(7rn/(jm) i/s , where m is the quantity of water 

 precipitated per cm. and n the number of nuclei per cm. on 

 which this water falls. I will add a few results showing the 

 relation of the s computed in this way and the observed 8 or 

 the s reduced from S. 



Figure 3 contains data both for S, '12S = s' and s and leads 

 to a curious consequence. The computed chords of the coro- 

 nas, s — a(7rn/6m) 1/3 are here not proportional to s= 2r sin 0, 

 but to s= 2R tan 0, where 29 is the angular diameter of the 

 coronas. This implies a diffraction equation reading tan 6 

 = l-22X/d. 



In figure 3 san 1/z is laid off as the abscissas and •12satan 9 



and '12 SV 1'8'R'a sin #, as the ordinates. If we confine our 

 attention to values within s = 14, where the readings are more 

 certain, and where there is less accentuated overlapping of 

 coronas, the graph .12S oscillates between two straight lines as 

 the coronas change from the red to the green types. The 

 slopes of these lines are respectivelv as 1*08 = 7SXfa and 

 •99 = 7S\/a, whence \ = -000047 and \ = -000043. These 

 should be blue and violet minima. 



The figure shows moreover that compared with the graph 

 for -12 S =60 tan 0, the curve for sin 6 is in series 1 quite out 

 of the question, as already specified. The results for other 

 independent series, 2, 3, are given in figure 4, in the same way. 

 Curiously enough, series 2 and 3, which should be identical with 

 1, fail to coincide with it in the region of higher coronas. In 

 these series the graph s a sin 6 (not shown) would more nearly 

 express the results, though the agreement is far from satisfac- 

 tory. 



